// Copyright (c) 2021, gottingen group.
// All rights reserved.
// Created by liyinbin lijippy@163.com
//
// This file provides city_hash64() and related functions.
//
// It's probably possible to create even faster hash functions by
// writing a program that systematically explores some of the space of
// possible hash functions, by using SIMD instructions, or by
// compromising on hash quality.

#include "abel/hash/internal/city.h"

#include <string.h>  // for memcpy and memset
#include <algorithm>
#include "abel/base/profile.h"
#include "abel/system/endian.h"
#include "abel/atomic/unaligned_access.h"

namespace abel {

namespace hash_internal {

#ifdef ABEL_SYSTEM_BIG_ENDIAN
#define uint32_in_expected_order(x) (abel::bit_swap32(x))
#define uint64_in_expected_order(x) (abel::bit_swap64(x))
#else
#define uint32_in_expected_order(x) (x)
#define uint64_in_expected_order(x) (x)
#endif

static uint64_t fetch64(const char *p) {
    return uint64_in_expected_order(ABEL_INTERNAL_UNALIGNED_LOAD64(p));
}

static uint32_t fetch32(const char *p) {
    return uint32_in_expected_order(ABEL_INTERNAL_UNALIGNED_LOAD32(p));
}

// Some primes between 2^63 and 2^64 for various uses.
static const uint64_t k0 = 0xc3a5c85c97cb3127ULL;
static const uint64_t k1 = 0xb492b66fbe98f273ULL;
static const uint64_t k2 = 0x9ae16a3b2f90404fULL;

// Magic numbers for 32-bit hashing.  Copied from Murmur3.
static const uint32_t c1 = 0xcc9e2d51;
static const uint32_t c2 = 0x1b873593;

// A 32-bit to 32-bit integer hash copied from Murmur3.
static uint32_t fmix(uint32_t h) {
    h ^= h >> 16;
    h *= 0x85ebca6b;
    h ^= h >> 13;
    h *= 0xc2b2ae35;
    h ^= h >> 16;
    return h;
}

static uint32_t rotate32(uint32_t val, int shift) {
    // Avoid shifting by 32: doing so yields an undefined result.
    return shift == 0 ? val : ((val >> shift) | (val << (32 - shift)));
}

#undef PERMUTE3
#define PERMUTE3(a, b, c) \
  do {                    \
    std::swap(a, b);      \
    std::swap(a, c);      \
  } while (0)

static uint32_t Mur(uint32_t a, uint32_t h) {
    // Helper from Murmur3 for combining two 32-bit values.
    a *= c1;
    a = rotate32(a, 17);
    a *= c2;
    h ^= a;
    h = rotate32(h, 19);
    return h * 5 + 0xe6546b64;
}

static uint32_t Hash32Len13to24(const char *s, size_t len) {
    uint32_t a = fetch32(s - 4 + (len >> 1));
    uint32_t b = fetch32(s + 4);
    uint32_t c = fetch32(s + len - 8);
    uint32_t d = fetch32(s + (len >> 1));
    uint32_t e = fetch32(s);
    uint32_t f = fetch32(s + len - 4);
    uint32_t h = len;

    return fmix(Mur(f, Mur(e, Mur(d, Mur(c, Mur(b, Mur(a, h)))))));
}

static uint32_t Hash32Len0to4(const char *s, size_t len) {
    uint32_t b = 0;
    uint32_t c = 9;
    for (size_t i = 0; i < len; i++) {
        signed char v = s[i];
        b = b * c1 + v;
        c ^= b;
    }
    return fmix(Mur(b, Mur(len, c)));
}

static uint32_t Hash32Len5to12(const char *s, size_t len) {
    uint32_t a = len, b = len * 5, c = 9, d = b;
    a += fetch32(s);
    b += fetch32(s + len - 4);
    c += fetch32(s + ((len >> 1) & 4));
    return fmix(Mur(c, Mur(b, Mur(a, d))));
}

uint32_t city_hash32(const char *s, size_t len) {
    if (len <= 24) {
        return len <= 12
               ? (len <= 4 ? Hash32Len0to4(s, len) : Hash32Len5to12(s, len))
               : Hash32Len13to24(s, len);
    }

    // len > 24
    uint32_t h = len, g = c1 * len, f = g;

    uint32_t a0 = rotate32(fetch32(s + len - 4) * c1, 17) * c2;
    uint32_t a1 = rotate32(fetch32(s + len - 8) * c1, 17) * c2;
    uint32_t a2 = rotate32(fetch32(s + len - 16) * c1, 17) * c2;
    uint32_t a3 = rotate32(fetch32(s + len - 12) * c1, 17) * c2;
    uint32_t a4 = rotate32(fetch32(s + len - 20) * c1, 17) * c2;
    h ^= a0;
    h = rotate32(h, 19);
    h = h * 5 + 0xe6546b64;
    h ^= a2;
    h = rotate32(h, 19);
    h = h * 5 + 0xe6546b64;
    g ^= a1;
    g = rotate32(g, 19);
    g = g * 5 + 0xe6546b64;
    g ^= a3;
    g = rotate32(g, 19);
    g = g * 5 + 0xe6546b64;
    f += a4;
    f = rotate32(f, 19);
    f = f * 5 + 0xe6546b64;
    size_t iters = (len - 1) / 20;
    do {
        uint32_t b0 = rotate32(fetch32(s) * c1, 17) * c2;
        uint32_t b1 = fetch32(s + 4);
        uint32_t b2 = rotate32(fetch32(s + 8) * c1, 17) * c2;
        uint32_t b3 = rotate32(fetch32(s + 12) * c1, 17) * c2;
        uint32_t b4 = fetch32(s + 16);
        h ^= b0;
        h = rotate32(h, 18);
        h = h * 5 + 0xe6546b64;
        f += b1;
        f = rotate32(f, 19);
        f = f * c1;
        g += b2;
        g = rotate32(g, 18);
        g = g * 5 + 0xe6546b64;
        h ^= b3 + b1;
        h = rotate32(h, 19);
        h = h * 5 + 0xe6546b64;
        g ^= b4;
        g = abel::bit_swap32(g) * 5;
        h += b4 * 5;
        h = abel::bit_swap32(h);
        f += b0;
        PERMUTE3(f, h, g);
        s += 20;
    } while (--iters != 0);
    g = rotate32(g, 11) * c1;
    g = rotate32(g, 17) * c1;
    f = rotate32(f, 11) * c1;
    f = rotate32(f, 17) * c1;
    h = rotate32(h + g, 19);
    h = h * 5 + 0xe6546b64;
    h = rotate32(h, 17) * c1;
    h = rotate32(h + f, 19);
    h = h * 5 + 0xe6546b64;
    h = rotate32(h, 17) * c1;
    return h;
}

// Bitwise right rotate.  Normally this will compile to a single
// instruction, especially if the shift is a manifest constant.
static uint64_t Rotate(uint64_t val, int shift) {
    // Avoid shifting by 64: doing so yields an undefined result.
    return shift == 0 ? val : ((val >> shift) | (val << (64 - shift)));
}

static uint64_t ShiftMix(uint64_t val) { return val ^ (val >> 47); }

static uint64_t HashLen16(uint64_t u, uint64_t v) {
    return hash128_to_64(uint128(u, v));
}

static uint64_t HashLen16(uint64_t u, uint64_t v, uint64_t mul) {
    // Murmur-inspired hashing.
    uint64_t a = (u ^ v) * mul;
    a ^= (a >> 47);
    uint64_t b = (v ^ a) * mul;
    b ^= (b >> 47);
    b *= mul;
    return b;
}

static uint64_t HashLen0to16(const char *s, size_t len) {
    if (len >= 8) {
        uint64_t mul = k2 + len * 2;
        uint64_t a = fetch64(s) + k2;
        uint64_t b = fetch64(s + len - 8);
        uint64_t c = Rotate(b, 37) * mul + a;
        uint64_t d = (Rotate(a, 25) + b) * mul;
        return HashLen16(c, d, mul);
    }
    if (len >= 4) {
        uint64_t mul = k2 + len * 2;
        uint64_t a = fetch32(s);
        return HashLen16(len + (a << 3), fetch32(s + len - 4), mul);
    }
    if (len > 0) {
        uint8_t a = s[0];
        uint8_t b = s[len >> 1];
        uint8_t c = s[len - 1];
        uint32_t y = static_cast<uint32_t>(a) + (static_cast<uint32_t>(b) << 8);
        uint32_t z = len + (static_cast<uint32_t>(c) << 2);
        return ShiftMix(y * k2 ^ z * k0) * k2;
    }
    return k2;
}

// This probably works well for 16-byte strings as well, but it may be overkill
// in that case.
static uint64_t HashLen17to32(const char *s, size_t len) {
    uint64_t mul = k2 + len * 2;
    uint64_t a = fetch64(s) * k1;
    uint64_t b = fetch64(s + 8);
    uint64_t c = fetch64(s + len - 8) * mul;
    uint64_t d = fetch64(s + len - 16) * k2;
    return HashLen16(Rotate(a + b, 43) + Rotate(c, 30) + d,
                     a + Rotate(b + k2, 18) + c, mul);
}

// Return a 16-byte hash for 48 bytes.  Quick and dirty.
// Callers do best to use "random-looking" values for a and b.
static std::pair<uint64_t, uint64_t> WeakHashLen32WithSeeds(uint64_t w, uint64_t x,
                                                            uint64_t y, uint64_t z,
                                                            uint64_t a, uint64_t b) {
    a += w;
    b = Rotate(b + a + z, 21);
    uint64_t c = a;
    a += x;
    a += y;
    b += Rotate(a, 44);
    return std::make_pair(a + z, b + c);
}

// Return a 16-byte hash for s[0] ... s[31], a, and b.  Quick and dirty.
static std::pair<uint64_t, uint64_t> WeakHashLen32WithSeeds(const char *s, uint64_t a,
                                                            uint64_t b) {
    return WeakHashLen32WithSeeds(fetch64(s), fetch64(s + 8), fetch64(s + 16),
                                  fetch64(s + 24), a, b);
}

// Return an 8-byte hash for 33 to 64 bytes.
static uint64_t HashLen33to64(const char *s, size_t len) {
    uint64_t mul = k2 + len * 2;
    uint64_t a = fetch64(s) * k2;
    uint64_t b = fetch64(s + 8);
    uint64_t c = fetch64(s + len - 24);
    uint64_t d = fetch64(s + len - 32);
    uint64_t e = fetch64(s + 16) * k2;
    uint64_t f = fetch64(s + 24) * 9;
    uint64_t g = fetch64(s + len - 8);
    uint64_t h = fetch64(s + len - 16) * mul;
    uint64_t u = Rotate(a + g, 43) + (Rotate(b, 30) + c) * 9;
    uint64_t v = ((a + g) ^ d) + f + 1;
    uint64_t w = abel::bit_swap64((u + v) * mul) + h;
    uint64_t x = Rotate(e + f, 42) + c;
    uint64_t y = (abel::bit_swap64((v + w) * mul) + g) * mul;
    uint64_t z = e + f + c;
    a = abel::bit_swap64((x + z) * mul + y) + b;
    b = ShiftMix((z + a) * mul + d + h) * mul;
    return b + x;
}

uint64_t city_hash64(const char *s, size_t len) {
    if (len <= 32) {
        if (len <= 16) {
            return HashLen0to16(s, len);
        } else {
            return HashLen17to32(s, len);
        }
    } else if (len <= 64) {
        return HashLen33to64(s, len);
    }

    // For strings over 64 bytes we hash the end first, and then as we
    // loop we keep 56 bytes of state: v, w, x, y, and z.
    uint64_t x = fetch64(s + len - 40);
    uint64_t y = fetch64(s + len - 16) + fetch64(s + len - 56);
    uint64_t z = HashLen16(fetch64(s + len - 48) + len, fetch64(s + len - 24));
    std::pair<uint64_t, uint64_t> v = WeakHashLen32WithSeeds(s + len - 64, len, z);
    std::pair<uint64_t, uint64_t> w = WeakHashLen32WithSeeds(s + len - 32, y + k1, x);
    x = x * k1 + fetch64(s);

    // Decrease len to the nearest multiple of 64, and operate on 64-byte chunks.
    len = (len - 1) & ~static_cast<size_t>(63);
    do {
        x = Rotate(x + y + v.first + fetch64(s + 8), 37) * k1;
        y = Rotate(y + v.second + fetch64(s + 48), 42) * k1;
        x ^= w.second;
        y += v.first + fetch64(s + 40);
        z = Rotate(z + w.first, 33) * k1;
        v = WeakHashLen32WithSeeds(s, v.second * k1, x + w.first);
        w = WeakHashLen32WithSeeds(s + 32, z + w.second, y + fetch64(s + 16));
        std::swap(z, x);
        s += 64;
        len -= 64;
    } while (len != 0);
    return HashLen16(HashLen16(v.first, w.first) + ShiftMix(y) * k1 + z,
                     HashLen16(v.second, w.second) + x);
}

uint64_t city_hash64_with_seed(const char *s, size_t len, uint64_t seed) {
    return city_hash64_with_seeds(s, len, k2, seed);
}

uint64_t city_hash64_with_seeds(const char *s, size_t len, uint64_t seed0,
                                uint64_t seed1) {
    return HashLen16(city_hash64(s, len) - seed0, seed1);
}

}  // namespace hash_internal

}  // namespace abel
